We have recently reported the presence of two homodisperse, methylated, cytoplasmic RNAs, of small molecular weight, and short half-life, in human carcinoma cells. With the final goal of learning about their role and regulation in the cell, we would like to investigate their possible relationship with protein synthesis by drug inhibition studies, assays for particle association, and in vitro studies in a polypeptide synthesis system. Their structure will be analyzed mostly by T1 RNAase fingerprints. Their relationship with cell growth will be investigated by studying their metabolism in resting and growing cells, cells in the transition from resting to the growing state, and in various phases of the cell cycle. The number of their genes will be estimated. Neoplastic, transformed and normal cells will be compared in reference to these two RNAs.